test: group examples into per-category folders

Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.

examples/diagnostics/1186-diagnostics-atomic-cas-ordering.sx

@@ -0,0 +1,12 @@
+// Atomic compare-exchange dual-ordering validation: the FAILURE ordering may not
+// be stronger than the SUCCESS ordering (LLVM rule). Here failure=.seq_cst (rank
+// 3) is stronger than success=.relaxed (rank 0) → loud diagnostic, not invalid IR.
+// Calls the intrinsic directly so the diagnostic span is stable (user file, not
+// the lib forward site). Stream A (atomics) A.2.
+#import "modules/std.sx";
+#import "modules/std/atomic.sx";
+
+main :: () {
+    n : i64 = 0;
+    _ := atomic_cmpxchg(i64, @n, 0, 1, .relaxed, .seq_cst);
+}